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Question Relating to CIC filters

 
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cbarberis



Joined: 01 Oct 2003
Posts: 171
Location: Punta Gorda, Florida USA

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Question Relating to CIC filters
PostPosted: Sat Nov 07, 2009 2:50 pm     Reply with quote

Hello,

I am interested in applying a CIC (Cascaded Integrator-Comb) filter algorithm on a PIC micro. I looked at some info on the web. I found much of it somewhat esoteric and not as clear as I would like, in order to implement my own code. Most of the stuff I found was in the VHDL language which I do not use or understand that well. I was wondering if any of you have any C code snippets that actually implement the CIC filter functions, or if you can point the way to such information.

I am aware that the past October issue of Circuit Cellar did have an article on this subject, however it clearly did not answer my needs.
FvM



Joined: 27 Aug 2008
Posts: 2337
Location: Germany

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PostPosted: Sun Nov 08, 2009 2:16 am     Reply with quote

By design, the word length of a CIC filter is different in individual stages and possibly exceeds the size of the data types provided by a C compiler (typically int32 with 8-bit compilers). It's easy, to achieve a parameterizable (in decimation ratio, order and input/output word length) CIC filter design for FPGA, but for a uP, a full-featured macro assembler would be needed.

Did you calculate the required word lengths for your application?

P.S.: A first order CIC decimator isn't but a simple boxcar averager. You don't need to understand CIC theory to implement it.
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